danger attached to such an errand of mercy. These Germans would neither understand their motives, nor think of sparing them if an oppor, tunity arose whereby the mistake of the first unlucky, undersea craft could be repaired.
"What was it those gunners had with them, but failed to drop overboard?" asked Jack, pointing as he spoke to some men who were placing some object under cover again.
"I don't exactly know," his chum replied, "but I've an idea it may have been what they call a depth bomb. It was possibly intended to drop it down after we'd passed the spot, if there were no actual signs that the submarine had been destroyed. But when the captain took note of all that oil on the sea he had no doubt about it; so the bomb wasn't used, after all."
"What is a depth bomb, Mr. Raymond?" asked a woman standing beside the two air service boys.
"It's a new invention that they use with good results in hunting these sea slinkers," she was told. "When a destroyer sights a periscope it speeds to the spot at the rate of nearly forty miles an hour. If the German submerges in a hurry so the destroyer's crew can't shoot his periscope away, and so destroy him, then they drop over one of those bombs.
